Vehicles having a regenerating function to recover and reuse kinetic energy generated during braking as electric energy with a power generator have been recently developed. This regenerating function allows effective use of the kinetic energy that has not been used, and hence allows energy saving of the vehicle.
FIG. 17 is a schematic circuit diagram of power supply device 501 described in Patent Document 1. Power supply device 501 is connected to an alternating-current (AC) power source. AC power supply 101 for driving an induction motor with the AC power source is connected to converter 111. Converter 111 converts an AC power output from AC power supply 101 into direct-current (DC) power, and outputs the DC power from positive output terminal 111A and negative output terminal 111B. Converter 111 has AC reactor 103, bridge rectifier 105, smoothing reactor 107, and smoothing capacitor 109. Switch 113 has branch contacts 115 and 117 and common contact 118. Common contact 118 is connected selectively to branch contacts 115 and 117. Positive output terminal 111A of converter 111 is connected to branch contact 115 of switch 113. Branch contact 117 of switch 113 is connected to negative output terminal 111B of converter 111. The anode of diode 119 and one end of capacitor 121 are connected to common contact 118 of switch 113. Capacitor 121 is an electric double layer capacitor having a large capacity. The cathode of diode 119 and another end of capacitor 121 are connected to positive terminal 123A of inverter 123. Negative output terminal 111B of converter 111 is connected to negative terminal 123B of the inverter. Diode 119 and capacitor 121 are connected in parallel to each other. Inverter 123 includes a bridge circuit having plural transistors and plural flywheel diodes. Induction motor 125 is connected to terminals 123C of inverter 123.
An operation of power supply device 501 will be described below. First, when induction motor 125 starts or accelerates, switch 113 connects branch contact 115 to common contact 118. Thus, the AC power from AC power supply 101 is converted into DC power by converter 111, and the DC power is input to inverter 123 via switch 113 and diode 119. At this moment, capacitor 121 stores no power. The DC power input to inverter 123 is converted into AC power and is supplied to induction motor 125. Induction motor 125 is thus driven by AC power supply 101.
When induction motor 125 decelerates, switch 113 is switched to connect branch contact 117 to common contact 118. At this moment, induction motor 125 operates as a power generator to generate AC power. The generated AC power is converted into DC power by inverter 123. Capacitor 121 stored the DC power.
Then, when induction motor 125 accelerates again, switch 113 is switched to connect branch contact 115 to common contact 118. Thus, converter 111 is connected to capacitor 121 in series. Both the power stored in capacitor 121 and the power output from AC power supply 101 via converter 111 are supplied to induction motor 125 via inverter 123. Thus, power supply device 501 has a regenerating function, and reduces the power supplied from AC power supply 101 to induction motor 125.
Power supply device 501 can be used for an electric train including induction motor 125 driven by AC power supply 101, but cannot be used for ordinary automobile for the following reason. If power supply device 501 is applied to the ordinary automobile, a power generator (alternator) corresponds to AC power supply 101. Induction motor 125 operates as the power generator during deceleration, so that induction motor 125 corresponds to another power generator. Therefore, power supply device 501 is applicable to an electric train including two power generators. However, the ordinary automobile includes only one power generator, so that power supply device 501 is not applicable to the automobile and does not provide the automobile with the regenerating function.    Patent Document 1: JP3678582B